Tire for two-wheeled automotive vehicle

ABSTRACT

[Object] A tire, for a two-wheeled automotive vehicle, which is excellent in ride comfort and steering stability, is provided. 
     [Solution] A tire  12  for a two-wheeled automotive vehicle includes a carcass  20  that is extended on and between one of beads  18  and the other of the beads  18  along inner sides of a tread  14  and sidewalls  16 . The carcass  20  includes a first ply  34  and a second ply  36  that is layered outward of the first ply  34 . The first ply  34  is turned up around the beads  18  from an inner side toward an outer side in an axial direction. By the turning-up, the first ply  34  includes a main portion  34   a  and turned-up portions  34   b . The second ply  36  is turned back around the beads  18  from the outer side toward the inner side in the axial direction. By the turning-back, the second ply  36  includes a main portion  36   a  and turned-back portions  36   b.

TECHNICAL FIELD

The present invention relates to pneumatic tires that are to be mountedto two-wheeled automotive vehicles.

BACKGROUND ART

FIG. 4 shows a conventional tire 1 that is to be mounted to a frontwheel of a two-wheeled automotive vehicle. The tire 1 is disclosed inJP2013-35540. The tire 1 includes a first carcass ply 2 and a secondcarcass ply 3. The first carcass ply 2 is turned up around beads 4 fromthe inner side toward the outer side. The second carcass ply 3 is notwound around the beads 4. The second carcass ply 3 covers end portionsof the first carcass ply 2 that is turned up. The tire 1 includes thefirst carcass ply 2 and the second carcass ply 3, whereby stiffness isappropriately obtained.

CITATION LIST Patent Literature

Patent Literature 1: JP2013-35540

Patent Literature 2: JP01-262205

Patent Literature 3: JP2010-36695

Patent Literature 4: JP02-155812

Patent Literature 5: JP2000-62416

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The tire 1 was mounted to a two-wheeled automotive vehicle and a runningtest was conducted. In the running test for the tire 1, improvement ofstiffness was confirmed. By the improvement of stiffness, ride comfortand steering stability are improved. However, it was confirmed that adegree of improvement in stiffness was various among the tires 1 whichwere produced as samples according to the same specifications. Inparticular, it was confirmed that the variation was likely to occur inthe tire 1 in which the radius of curvature of a tread 5 was small. Theinventors attempted to improve the tire 1 in various manners in order tostably obtain an effect of improving stiffness.

An object of the present invention is to provide a tire, for atwo-wheeled automotive vehicle, which is excellent in ride comfort andsteering stability.

Solution to the Problems

A pneumatic tire, for a two-wheeled automotive vehicle, according to thepresent invention includes: a tread; a pair of sidewalls; a pair ofbeads; and a carcass. The sidewalls extend almost inward from ends,respectively, of the tread in a radial direction. The beads are disposedalmost inward of the sidewalls, respectively, in the radial direction.The carcass is extended on and between one of the beads and the other ofthe beads along inner sides of the tread and the sidewalls. The carcassincludes a first ply and a second ply that is layered outward of thefirst ply. The first ply is turned up around the beads from an innerside toward an outer side in an axial direction. By the first ply beingturned up, the first ply includes a main portion and turned-up portions.The second ply is turned back around the beads from the outer sidetoward the inner side in the axial direction. By the second ply beingturned back, the second ply includes a main portion and turned-backportions.

Preferably, a height H from an inner end P of the second ply that isturned back around the beads, to a turn-back end, is greater than orequal to 10 mm and not greater than 20 mm.

Preferably, each of the beads includes a core and an apex that extendsoutward from the core in the radial direction. The core has a bottomsurface that is formed as a plane that faces inward in the radialdirection.

Preferably, a ratio BW/SW of a width BW of the bottom surface to a seatsurface width SW of a seat surface which contacts with a seat surface ofa normal rim, is greater than or equal to 0.4 and not greater than 0.7.

Preferably, a radius of curvature of the tread at an equator plane, isgreater than or equal to 50 mm and not greater than 150 mm.

Advantageous Effects of the Invention

In the tire, for a two-wheeled automotive vehicle, according to thepresent invention, the carcass has the first ply and the second ply,whereby stiffness is appropriately improved. The tire is excellent inride comfort and steering stability. The second ply is turned backaround the beads, whereby an effect of improving stiffness is stablyobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a pneumatic tire according to oneembodiment of the present invention.

FIG. 2 is a cross-sectional view of a part of a pneumatic tire accordingto another embodiment of the present invention.

FIG. 3 illustrates (a) a structure of a tire according to a comparativeexample, and (b) a structure of a tire according to another comparativeexample.

FIG. 4 is a cross-sectional view of a part of a conventional pneumatictire.

DESCRIPTION OF EMBODIMENTS

The following will describe in detail the present invention based onpreferred embodiments with reference where appropriate to theaccompanying drawing.

FIG. 1 is a cross-sectional view of a pneumatic tire 12 according to oneembodiment of the present invention. The tire 12 is mounted to a frontwheel of a two-wheeled automotive vehicle. In FIG. 1, the up-downdirection represents the radial direction of the tire 12, the right-leftdirection represents the axial direction of the tire 12, and thedirection perpendicular to the drawing sheet represents thecircumferential direction of the tire 12. An alternate long and shortdash line CL in FIG. 1 represents the equator plane of the tire 12. Thetire 12 has a shape which is almost bilaterally symmetric about theequator plane. A solid line BL is a straight line that extends in theaxial direction, and represents a bead base line. The bead base line isa line that defines a rim diameter of a normal rim on which the tire 12is mounted (see JATMA).

The tire 12 includes a tread 14, sidewalls 16, clinches 17, beads 18, acarcass 20, a belt 22, a band 24, an inner liner 26, and chafers 27. Thetire 12 is a tubeless type pneumatic tire.

The tread 14 is formed of crosslinked rubber, and has a shape thatprojects outward in the radial direction. The tread 14 forms a treadsurface 28 that can contact with a road surface. An arrow R in FIG. 1represents a radius of curvature of the tread 14. The radius R ofcurvature is measured along the tread surface 28 at the equator plane.Grooves may be formed in the tread surface 28, thereby forming a treadpattern, which is not shown.

The sidewalls 16 extend from the ends of the tread 14 almost inward inthe radial direction. The sidewalls 16 are formed of crosslinked rubber.The sidewalls 16 absorb impact from a road surface due to deformation.The sidewalls 16 prevent the carcass 20 from being damaged.

The clinches 17 are disposed almost inward of the sidewalls 16 in theradial direction. The clinches 17 are disposed outward of the beads 18and the carcass 20 in the axial direction. The clinches 17 are formed ofcrosslinked rubber excellent in wear resistance. The clinches 17 arebrought into contact with flanges of a rim.

The beads 18 are disposed inward of the sidewalls 16 in the radialdirection. The beads 18 are disposed inward of the clinches 17 in theaxial direction. Each bead 18 includes a core 30 and an apex 32 thatextends outward from the core 30 in the radial direction. The core 30 isformed such that a non-stretchable wire is wound so as to bering-shaped. A steel wire is typically used for the core 30. The apex 32is tapered outward in the radial direction. The apex 32 is formed ofhighly hard crosslinked rubber.

For the beads 18, a cable bead structure in which the cross-sectionalshape of the core 30 is round is used. Around a core wire, another wireis helically wound, thereby forming the core 30. Since the cable beadstructure is used, rotation of the cores 30 according to deformation ofside portions of the tire 12 is facilitated. The tire 12 is excellent intransient characteristics in cornering. The tire 12 is excellent insteering stability in cornering.

The carcass 20 is extended on and between the beads 18 on both sides,along the inner sides of the tread 14 and the sidewalls 16. The carcass20 includes a first ply 34 and a second ply 36. The first ply 34 iswound around the beads 18 from the inner side toward the outer side inthe axial direction. The second ply 36 is layered outward of the firstply 34 in the radial direction. The second ply 36 is wound around thebeads 18 from the outer side toward the inner side in the axialdirection.

The first ply 34 is formed of a first carcass cord and topping rubber,which are not shown. The first carcass cord tilts relative to theequator plane. An absolute value of a tilt angle thereof relative to theequator plane is greater than or equal to 60° and not greater than 90°.The second ply 36 is formed of a second carcass cord and topping rubber.The second carcass cord tilts relative to the equator plane. An absolutevalue of a tilt angle thereof relative to the equator plane is greaterthan or equal to 60° and not greater than 90°. In other words, the tire12 is a radial tire. In the tire 12, a direction in which the firstcarcass cord tilts and a direction in which the second carcass cordtilts are opposite to each other with respect to the equator plane. Theabsolute value of the tilt angle of the first carcass cord and theabsolute value of the tilt angle of the second carcass cord are equal toeach other. The first carcass cord and the second carcass cord are eachformed of an organic fiber in general. Preferable examples of theorganic fiber include polyester fibers, nylon fibers, rayon fibers,polyethylene naphthalate fibers, and aramid fibers.

The belt 22 is disposed outward of the carcass 20 in the radialdirection. The belt 22 is layered over the carcass 20. The belt 22reinforces the carcass 20. The belt 22 inhibits protrusion of the tread14 in high speed running. The belt 22 allows improvement of high speeddurability and uniformity. The belt 22 includes multiple belt cordsaligned with each other, and topping rubber. The belt cords tiltrelative to the equator plane. An absolute value of a tilt angle isgreater than or equal to 10° and not greater than 35°. A material of thebelt cords is preferably an organic fiber. For the belt cords, steel maybe used. The belt 22 may include an inner layer and an outer layer. Whenthe belt includes the inner layer and the outer layer, a direction inwhich the belt cords of the inner layer tilt and a direction in whichthe belt cords of the outer layer tilt are opposite to each other.Further, the tire 12 may not include the belt 22.

The band 24 is layered outward of the carcass 20 in the radialdirection. The band 24 is layered outward of the belt 22 in the radialdirection. The band 24 includes a cord and topping rubber, which are notshown. The cord extends substantially in the circumferential direction,and is helically wound. The band 24 has a so-called jointless structure.The cord holds the tire 12 in the radial direction. The band 24 inhibitslifting of the belt 22. The cord is formed of an organic fiber ingeneral. Preferable examples of the organic fiber include nylon fibers,polyester fibers, rayon fibers, polyethylene naphthalate fibers, andaramid fibers. Further, the tire 12 may not include the band 24.

The inner liner 26 is joined to the inner circumferential surface of thecarcass 20. The inner liner 26 is formed of crosslinked rubber. For theinner liner 26, rubber excellent in airtightness is used. The innerliner 26 acts to maintain an internal pressure of the tire 12.

The chafers 27 are disposed near the beads 18. When the tire 12 ismounted on a rim, the chafers 27 contact with the rim. Portions near thebeads 18 are protected due to the contact. In the present embodiment,the chafers 27 are integrated with the clinches 17, respectively.Therefore, the material of the chafers 27 is the same as the material ofthe clinches 17. The chafers 27 may be formed of a fabric and rubberimpregnated into the fabric.

As shown in FIG. 1, the first ply 34 is turned up around the beads 18from the inner side toward the outer side in the axial direction. By theturning-up, the first ply 34 includes a main portion 34 a and turned-upportions 34 b. The turned-up portions 34 b have turn-up ends 34 cpositioned at the outer ends in the radial direction. The turn-up ends34 c are disposed inward of the tread 14.

The second ply 36 is turned back around the beads 18 from the outer sidetoward the inner side in the axial direction. By the turning-back, thesecond ply 36 includes a main portion 36 a and turned-back portions 36b. The turned-back portions 36 b have turn-back ends 36 c positioned atthe outer ends in the radial direction. The turn-back ends 36 c are eachdisposed inward of the apex 32 in the axial direction. The main portion36 a is extended on and between the axially outer side portion of one ofthe beads 8 and the axially outer side portion of the other of thebeads. The second ply 36 that has the main portion 36 a is referred toas a floating ply.

In FIG. 1, a point P represents a radially inner end of the second ply36 that is turned back around each bead 18. A double-headed arrow Hrepresents a height from the inner end P to the turn-back end 36 c. Theheight H is measured as a distance in a straight line in the radialdirection.

In the tire 12, in the main portion 34 a of the first ply 34, a tensileforce is generated between the paired beads 18 on the side inward of thebeads 18 in the axial direction. In the main portion 36 a of the secondply 36, a tensile force is generated between the paired beads 18 on theside outward of the beads 18 in the axial direction. A tensile force isgenerated in the carcass 20 on both the side inward of the paired beads18 in the axial direction, and the side outward of the paired beads 18in the axial direction. The main portion 34 a and the main portion 36 ain each of which a tensile force is generated surround the beads 18. Thecarcass 20 allows stiffness of the tire 12 to be appropriately improvedin a range between one of the beads 18 and the other of the beads 18. Inthe tire 12, the carcass 20 allows reduction of the thickness (thicknessfrom the inner side surface of the inner liner 26 to the outer surfaceof each sidewall 16) of each sidewall portion, thereby improvingstiffness. The carcass 20 can contribute to reduction in weight of thetire 12 and reduction of fuel consumption.

As described above, a tensile force is generated between the pairedbeads 18 in the main portion 36 a of the second ply 36. The second ply36 includes the turned-back portions 36 b, whereby the second ply 36 isassuredly fixed. Also when pressurizing and heating are performed invulcanization process, the second ply 36 is inhibited from beingdisplaced. The tire 12 having the turned-back portions 36 b allows aneffect of improving stiffness to be stably obtained.

In this viewpoint, the height H from the inner end P to the turn-backend 36 c is preferably greater than or equal to 10 mm, and morepreferably greater than or equal to 15 mm. Meanwhile, when the height His excessively increased, stiffness of the tire 12 is increased toreduce ride comfort. In this viewpoint, the height H is preferably notgreater than 40 mm, more preferably not greater than 30 mm, andparticularly preferably not greater than 25 mm.

In a two-wheeled automotive vehicle, its body is tilted inward incornering. In order to facilitate the cornering, the tire 12 has thetread 14 having a small radius R of curvature. In straight running, acenter region C of the tread 14 (tread surface 28) mainly contacts withthe ground. In cornering, a shoulder region S positioned outward of thecenter region C in the axial direction mainly contacts with the ground.In general, in a tire for a passenger car which is a four-wheeledautomotive vehicle, the radius R of curvature at the equator plane isfrom 500 mm to 1000 mm. Meanwhile, in a tire for a two-wheeledautomotive vehicle, the radius R of curvature at the equator plane isgreater than or equal to 50 mm and not greater than 150 mm in general.The radius of curvature of the tire 12 is very small as compared to thatof a tire for a four-wheeled automotive vehicle.

In a method for manufacturing the tire 14, components forming the tread14, the sidewalls 16, the clinches 17, the beads 18, the carcass 20, thebelt 22, the band 24, the inner liner 26, and the chafers 27 arecombined to perform forming. By the forming, an unvulcanized green tireis obtained. The green tire is pressurized and heated with a mold and abladder. In the mold, rubber flows and crosslinking is performed toobtain the tire 12.

As described above, in the tire 12, the radius R of curvature of thetread 14 is small. In the green tire for the tire 12, a tensile forceacts so as to draw the axial end portions of the first ply 34 and thesecond ply 36 toward the center region of the tread 14. The tensileforce becomes high particularly when pressurizing and heating areperformed. In the tire 12, the second ply 36 is turned back around thebeads 18. The second ply 36 is disposed and fixed between the cores 30and a wall surface of the mold when pressurizing and heating areperformed. Movement of the second ply 36 is inhibited. Since movement ofthe second ply 36 is inhibited, an effect of improving stiffness isstably obtained. The tire 12 is stable in quality.

To the tire 12 mounted to a two-wheeled automotive vehicle, such a heavyload as applied to a tire of a four-wheeled automotive vehicle is notapplied. Therefore, the second ply 36 need not be turned back around thecores 30 in order to assure stiffness of the tire 12. On the contrary,if the second ply 36 is turned back around the cores 30, productivity isreduced. Therefore, in a tire for a two-wheeled automotive vehicle, thesecond ply 36 is not turned back around the cores 30 in general.Meanwhile, according to the present invention, the second ply 36 isintentionally turned back around the cores 30 in order to stably obtainan effect of improving stiffness of the tire 12.

In the present invention, the dimensions and angles of the components ofthe tire 12 are measured in a state where the tire 12 is mounted on anormal rim, and is inflated with air to a normal internal pressure.During the measurement, no load is applied to the tire 12. In thedescription herein, the normal rim represents a rim which is specifiedaccording to the standard with which the tire 12 complies. The “standardrim” in the JATMA standard, the “Design Rim” in the TRA standard, andthe “Measuring Rim” in the ETRTO standard are included in the normalrim. In the description herein, the normal internal pressure representsan internal pressure which is specified according to the standard withwhich the tire 12 complies. The “maximum air pressure” in the JATMAstandard, the “maximum value” recited in “TIRE LOAD LIMITS AT VARIOUSCOLD INFLATION PRESSURES” in the TRA standard, and the “INFLATIONPRESSURE” in the ETRTO standard are included in the normal internalpressure.

FIG. 2 illustrates a part of another tire 42 according to the presentinvention. For the tire 42, components different from the components ofthe tire 12 will be described. Description of the same components as inthe tire 12 is not given. Further, the same components as in the tire 12will be described by using the same reference numerals as used for thetire 12.

The tire 42 includes beads 44 instead of the beads 18. The tire 42 hasthe same structure as the tire 12 except that the tire 42 has the beads44. Each bead 44 includes a core 46 and an apex 48 that extends outwardfrom the core 46 in the radial direction. The apex 48 is tapered outwardin the radial direction. The apex 48 is formed of a highly hardcrosslinked rubber.

The core 46 is formed such that a non-stretchable wire is wound so as tobe ring-shaped. A steel wire is typically used for the core 46. On thecross-section of the core 46, a plurality of non-stretchable wires arealigned in the axial direction at almost regular intervals, and aplurality of non-stretchable wires are aligned also in the radialdirection at almost regular intervals. The aligned non-stretchable wiresare covered by coating rubber. The cross-section of the core 46 hasalmost a rectangular shape. The beads 44 have a strand bead structure.In the description herein, the strand bead structure includes a corethat is formed such that one non-stretchable wire is wound. In otherwords, the strand bead structure includes a so-called single windingbead structure. In the core 46, rotation is inhibited. The core 46contributes to improvement of stiffness of the tire 42.

In FIG. 2, an alternate long and two short dashes line F represents theshape of a rim. A state in which the tire 42 is mounted on a normal rim,is represented. A point Pt represents a position of a toe of the tire42. A point Pc represents a point of intersection of a straight linethat extends along a seat surface and a straight line that extends alonga contact surface that contacts with a flange. In FIG. 2, adouble-headed arrow BW represents a width of a bottom surface 46 a ofthe core 46. The width BW is measured along the bottom surface 46 a. Adouble-headed arrow SW represents a seat surface width of the seatsurface that contacts with a seat surface of a rim. The seat surfacewidth SW is measured in a state where the tire is mounted on the rim.The seat surface width SW is measured as a distance in a straight linefrom the toe Pt to the point Pc of intersection.

The core 46, which has an almost rectangular cross-section, includes thebottom surface 46 a that faces inward in the radial direction. For thetire 42, when the green tire is vulcanized, the second ply 36 isdisposed between the bottom surface 46 a of the core 46 and a wallsurface of a mold. By the bottom surface 46 a being provided, the secondply 36 is fixed more firmly. By the core 46 being provided, an effect ofimproving stiffness of the tire 42 can be more stably obtained.

In this viewpoint, the width BW of the bottom surface 46 a of the core46 is preferably great. A ratio BW/SW is preferably greater than orequal to 0.4, and more preferably greater than or equal to 0.5. The tire42 includes the clinches 17 and the chafers 27 that protect the beads44. In order to protect the beads 44, the BW/SW is preferably notgreater than 0.7, and is more preferably greater than or equal to 0.6.

Also in the tire 12 described above, in order to assuredly fix thesecond ply 36 between the cores 30 and a wall surface of a mold, eachcore 30 preferably has a bottom surface that faces inward in the radialdirection, which is not shown.

EXAMPLES

Hereinafter, effects of the present invention will become apparentaccording to examples. However, the present invention should not berestrictively construed based on the description of examples.

Example 1

A tire having a basic structure shown in FIG. 1 was prepared. The sizeof the tire was 120/70R17. The height H from the inner end P of thesecond ply that was turned back around the beads, to the turn-back endwas 20 mm. The beads had a cable bead structure, and the cross-sectionalshape of the core was round.

Comparative Example 1

A commercially available tire having a carcass structure shown in (b) ofFIG. 3 was prepared. The carcass of the tire had two carcass plies, andthe two carcass plies were turned up around each bead from the innerside toward the outer side in the axial direction. The other structurewas the same as for Example 1.

Comparative Example 2

A commercially available tire having a carcass structure shown in FIG. 4was prepared. The carcass of the tire had two carcass plies. The innercarcass ply was turned up around the beads from the inner side towardthe outer side in the axial direction. The outer carcass ply was aso-called floating ply, and was extended between the axially outer sideportions of the paired beads and was not turned back around the beads.The other structure was the same as for Example 1.

Comparative Example 3

A tire having a carcass structure shown in (a) of FIG. 3 was prepared.The carcass of the tire had two carcass plies. The inner carcass ply wasturned up around the beads from the inner side toward the outer side inthe axial direction. The outer carcass ply was a so-called floating ply,and was extended between the axially outer side portions of the pairedbeads and was not turned back around the beads. The ends of the outercarcass ply were positioned at the inner ends, in the radial direction,of the cores, respectively. The other structure was the same as forExample 1, thereby obtaining the tire.

Examples 2 to 4

Tires were each obtained in the same manner as for Example 1 except thatthe height H was as indicated in Table 1.

Examples 5 to 9

Tires having a bead structure shown in FIG. 2 were prepared. The heightH and the bead structure of each tire were as indicated in Table 2. Theratio BW/SW of the width BW of the bottom surface of the core, to theseat surface width SW was as indicated in Table 2. The other structurewas the same as for Example 1, thereby obtaining the tire.

[Evaluation in Disassembling]

The tires were disassembled, and the finished dimensions were measured.Difference between the finished dimension and a design value (targetvalue) was evaluated. Each evaluation result is indicated as an index inTables 1 and 2 with the evaluation result of Example 6 being 100. Thegreater the value of the evaluation result is, the higher the evaluationis.

[Performance of Actual Vehicle]

The tires were each mounted on a normal rim (17×MT3.50), and was mountedto a front wheel of a commercially available two-wheeled automotivevehicle having an engine displacement of 1000 cc (cm²). Air pressure ofeach tire was a normal internal pressure of 220 kPa. A commerciallyavailable tire was mounted to a rear wheel. The two-wheeled automotivevehicle was caused to run on a dry asphalt mountain road, and a sensoryevaluation for steering stability and ride comfort was made by a rider.Each evaluation result is indicated as an index in Tables 1 and 2 withthe evaluation result of Example 6 being 100. The greater the value ofthe evaluation result is, the higher the evaluation is.

TABLE 1 Evaluation result Comp. Comp. Comp. ex. 1 ex. 2 ex. 3 Ex. 2 Ex.1 Ex. 3 Ex. 4 Carcass FIG. FIG. FIG. FIG. FIG. FIG. FIG. structure 3 (b)4 3 (a) 1 1 1 1 Height H (mm) — —  0 10 20 30 40 Bead structure CableCable Cable Cable Cable Cable Cable bead bead bead bead bead bead beadEvaluation in 90 75 80 90 90 90 90 disassembling Performance of 50 80 8095 95 90 80 actual vehicle

TABLE 2 Evaluation result Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Carcass FIG. 2FIG. 2 FIG. 2 FIG. 2 FIG. 2 structure Height H (mm) 20 20 20 20 20 Beadstructure Strand Strand Strand Strand Strand bead bead bead bead beadRatio BW/SW 0.4 0.5 0.6 0.7 0.8 Evaluation in 95 100 100 95 85disassembling Performance of 98 100 100 98 90 actual vehicle

As indicated in Table 1 and Table 2, the evaluation of the tires ofexamples is higher than the evaluation of the tires of comparativeexample. This evaluation result clearly indicates that the presentinvention is superior.

INDUSTRIAL APPLICABILITY

The tire described above is widely applicable not only to front wheelsof two-wheeled automotive vehicles but also as pneumatic tires mountedto rear wheels.

DESCRIPTION OF THE REFERENCE CHARACTERS

-   -   12, 42 . . . tire    -   14 . . . tread    -   18, 44 . . . bead    -   20 . . . carcass    -   28 . . . tread surface    -   30, 46 . . . core    -   32, 48 . . . apex    -   34 . . . first ply    -   36 . . . second ply

1. A pneumatic tire for a two-wheeled automotive vehicle, the pneumatictire comprising: a tread; a pair of sidewalls; a pair of beads; and acarcass, wherein the sidewalls extend almost inward from ends,respectively, of the tread in a radial direction, the beads are disposedalmost inward of the sidewalls, respectively, in the radial direction,the carcass is extended on and between one of the beads and the other ofthe beads along inner sides of the tread and the sidewalls, the carcassincludes a first ply and a second ply that is layered outward of thefirst ply, the first ply is turned up around the beads from an innerside toward an outer side in an axial direction, and, by the first plybeing turned up, the first ply includes a main portion and turned-upportions, and the second ply is turned back around the beads from theouter side toward the inner side in the axial direction, and, by thesecond ply being turned back, the second ply includes a main portion andturned-back portions.
 2. The tire according to claim 1, wherein a heightH from an inner end of the second ply that is turned back around thebeads, to a turn-back end, is greater than or equal to 10 mm and notgreater than 20 mm.
 3. The tire according to claim 1, wherein each ofthe beads includes a core and an apex that extends outward from the corein the radial direction, and the core has a bottom surface that isformed as a plane that faces inward in the radial direction.
 4. The tireaccording to claim 3, wherein a ratio BW/SW of a width BW of the bottomsurface to a seat surface width SW of a seat surface which contacts witha seat surface of a normal rim, is greater than or equal to 0.4 and notgreater than 0.7.
 5. The tire according to claim 1, wherein a radius ofcurvature of the tread at an equator plane, is greater than or equal to50 mm and not greater than 150 mm.
 6. The tire according to claim 2,wherein each of the beads includes a core and an apex that extendsoutward from the core in the radial direction, and the core has a bottomsurface that is formed as a plane that faces inward in the radialdirection.
 7. The tire according to claim 2, wherein a radius ofcurvature of the tread at an equator plane, is greater than or equal to50 mm and not greater than 150 mm.
 8. The tire according to claim 3,wherein a radius of curvature of the tread at an equator plane, isgreater than or equal to 50 mm and not greater than 150 mm.
 9. The tireaccording to claim 4, wherein a radius of curvature of the tread at anequator plane, is greater than or equal to 50 mm and not greater than150 mm.